Washing machine

ABSTRACT

A washing machine includes a cabinet; an outer tub horizontally installed in the cabinet; an inner tub rotatably installed in the outer tub; and a planarized unit configured to planarize at least one of an inner surface of the outer tub and an outer surface of the inner tub, the inner surface of the outer tub and the outer surface of the inner tub facing with each other.

CROSS-REFERENCE TO RELATED APPLICATIONS

This nonprovisional application claims priority under 35 U.S.C. §119(a) on Patent Application No. 10-2007-0009653 filed in Korea on Jan. 30, 2007, the entire contents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a washing machine, and more particularly, to a washing machine capable of avoiding or reducing noise generation during a rotation of an inner tub.

2. Background of the Invention

In general, a washing machine, as shown in FIG. 1, includes a cabinet 10, an outer tub 20 received in the cabinet 10, and an inner tub 50 rotatably installed in the outer tub 20.

An opening 12 and a door 14 are disposed at the front surface of the cabinet 10 such that clothes to be washed or washed can be drawn in or out. The outer tub 20 is supported by a spring 22 and a damper 23 in the cabinet 10.

The outer tub 20 has a cylindrical shape with one side open. The inner tub 50 is rotatably installed in the outer tub 20. The inner tub 50 also has a cylindrical shape with one side open. A plurality of through holes 53 are formed in a circumferential surface of the inner tub 50. A plurality of lifts 55 are disposed at an inner surface of the inner tub 50 so as to lift laundries or clothes.

A driving motor 25 is coupled to a rear end portion of the outer tub 20 to rotate the inner tub 50. A drain passage 27 having a drain pump 28 is disposed below the outer tub 20 so as to drain water.

As shown in FIG. 2, at the inner surface of the rear end portion of the outer tub 20 are formed plane portions 33 and recess portions 35 recessed below the plane portions 33. Each plane portion 33 has a plane surface. Each recess portion 35 comprises linear ribs 36 protruding from a lower surface of the recess portion 35 to linearly extend along a radial direction of the outer tub 20, and arcuate ribs 37 protruding from the lower surface of the recess portion 35 to extend by a certain length along a circumferential direction of the outer tub 20.

As shown in FIG. 3, a frame 71 having a rotation shaft 73 at the center thereof is disposed at an outer surface of the rear end portion of the inner tub 50. At a rear end portion of the inner tub 50 are provided an end surface 64, an insertion portion 65 recessed into the end surface 64 in correspondence with the shape of the frame 71 such that the frame 71 can be inserted therein, and protrusions 67 backwardly protruding from the end surface 64. A plurality of through holes 68 are formed in the protrusion 67 such that inside and outside thereof can be communicated.

As shown in FIG. 4, both end portions at a sectional surface of the frame 71 are bent to be in contact with side surfaces of the insertion portion 65, and a central portion of the sectional surface of the frame 71 protrudes outwardly.

However, the related art washing machine has the configuration that the protrusions 67 are formed at the outer surface of the rear end portion of the inner tub 50, the plane portions 33 and the recess portions 35 are formed at the inner surface of the rear end portion of the outer tub 20, and the linear ribs 36 and the arcuate ribs 37 are formed in each of the recess portions 35. As a result, upon the rotation of the inner tub 50, noise due to air flow (i.e., air-bone noise) are generated drastically, which increases the overall driving noise.

SUMMARY OF THE INVENTION

Therefore, in order to solve the problem of the related art, an object of the present invention is to provide a washing machine capable of avoiding or reducing noise generation during a rotation of an inner tub.

Another object of the present invention is to provide a washing machine capable of avoiding or reducing noise generation without significantly changing the configuration thereof.

To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described herein, a washing machine includes a cabinet; an outer tub horizontally installed in the cabinet; an inner tub rotatably installed in the outer tub; and a planarized unit configured to planarize at least one of an inner surface of the outer tub and an outer surface of the inner tub, the inner surface of the outer tub and the outer surface of the inner tub facing with each other.

In another aspect of the present invention, a washing machine includes a cabinet; an outer tub horizontally installed in the cabinet; an inner tub rotatably installed in the outer tub; an outer tub planarized unit configured to planarize an inner surface of a rear end portion of the outer tub; and an inner tub planarized unit configured to planarize an outer surface of a rear end portion of the inner tub.

Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, and wherein:

FIG. 1 is a cross-sectional view of a related art washing machine;

FIG. 2 is a front cross-sectional view showing an inner surface of an outer tub of FIG. 1;

FIG. 3 is a side cross-sectional view showing an outer surface of an inner tub of FIG. 1;

FIG. 4 is a cross-sectional view taken along the line IV-IV of FIG. 3;

FIG. 5 is a cross-sectional view showing a washing machine in accordance with a first embodiment of the present invention;

FIG. 6 is a disassembled perspective view of the inner tub of FIG. 5;

FIG. 7 is a cross-sectional view taken along the line VII-VII of FIG. 6;

FIG. 8 is a cross-sectional view showing a washing machine in accordance with a second embodiment of the present invention;

FIG. 9 is a disassembled perspective view of an inner tub of FIG. 8;

FIG. 10 is a side cross-sectional view showing a coupled state of the inner tub of FIG. 9;

FIG. 11 is a cross-sectional view taken along the line XI-XI of FIG. 10;

FIG. 12 is a disassembled perspective view of an inner tub and a frame cover of a washing machine in accordance with a third embodiment of the present invention;

FIG. 13 is a partial cross-sectional view showing a coupled state between the inner tub and the frame cover of FIG. 12;

FIG. 14 is a cross-sectional view showing a washing machine in accordance with a fourth embodiment of the present invention;

FIG. 15 is a perspective view showing an inner surface of an outer tub taken along the line XV-XV of FIG. 14;

FIG. 16 is a perspective view showing a rear end portion of an outer tub of FIG. 15;

FIG. 17 is a cross-sectional view showing a washing machine in accordance with a fifth embodiment of the present invention;

FIG. 18 is a disassembled perspective view showing an inside of an outer tub taken along the line XVIII-XVIII of FIG. 17;

FIG. 19 is a cross-sectional view taken along the line XIX-XIX of FIG. 18;

FIG. 20 is a cross-sectional view showing a washing machine in accordance with a sixth embodiment of the present invention;

FIG. 21 is a disassembled perspective view showing an inside of an outer tub of FIG. 20; and

FIG. 22 is a disassembled perspective view showing an outside of an inner tub of FIG. 20.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

The present invention will now be described in detail with reference to the accompanying drawings, wherein the same reference numerals will be used to identify the same or similar elements throughout the several views. It should be noted that the drawings should be viewed in the direction of orientation of the reference numerals.

As shown in FIG. 5, a washing machine according to an embodiment of the present invention may comprise a cabinet 110, an outer tub 120 horizontally installed in the cabinet 110, an inner tub 160 rotatably installed in the outer tub 120, and an inner tub planarized unit 170 formed by planarizing an outer surface of the inner tub 160 such that concave-convex portions in an axial direction can be reduced, to restrain air noise from being generated during the rotation of the inner tub 160.

An opening 112 and a door 114 are disposed at the front surface of the cabinet 110. The outer tub 120 is supported by a spring 122 and a damper 124 in the cabinet 110. A driving motor 128 for rotating the inner tub 160 is installed at a rear end portion of the outer tub 120. A drain passage 125 having a drain pump 127 is formed below the outer tub 120.

The inner tub 160, as shown in FIG. 6, may comprise a cylindrical portion 162 having a certain diameter, and a rear end portion 172 perpendicularly disposed to block the rear side of the cylindrical portion 162. An opening having a diameter shorter than that of the cylindrical portion 162 is formed at the front surface of the cylindrical portion 162. A plurality of through holes 164 are formed through the cylindrical portion 162 such that inside and outside of the cylindrical portion 162 can communicate with each other. Lifts 165 for lifting clothes are disposed at an inner surface of the cylindrical portion 162.

The inner tub planarized unit 170 may include the rear end portion 172 of the inner tub 160 and a frame 181 coupled to the rear end portion 172.

The frame 181 is formed to be approximately triangular. Each edge thereof is formed to be arcuate inwardly as shown in FIG. 6. A rotation shaft 185 protrudes from the center of the frame 181 to be connected to the driving motor 128.

The frame 181, as shown in FIG. 7, may include a plate portion 183 forming a plate shape and a plurality of ribs 184 protruding from the inner surface of the plate portion 183.

The rear end portion 172 of the inner tub 160 may include plane portions 174 perpendicular to the cylindrical portion 162, and an insertion portion 177 recessed into the plane portions 174 in correspondence with the shape of the frame 181. Each of the plane portions 174 has a plurality of through holes 175 such that inside and outside of the inner tub 160 can communicate with each other.

In accordance with such configuration, when the frame 181 is inserted into the insertion portion 177 under the condition that the rotation shaft 185 is positioned in a rear direction, an outer surface of the plate portion 183 of the frame 181 is substantially coplanar with the outer surface of the rear end portion 172 of the inner tub 160, namely, the surface where the plane portions 174 are formed. Accordingly, noise generated due to an air flow during the rotation of the inner tub 160 can be prevented or significantly reduced.

Hereinafter, a washing machine in accordance with a second embodiment of the present invention will be described with reference to FIGS. 8 to 11. For the sake of explanation, the same reference numerals will be given for the same configuration and components as the aforementioned ones, and detailed description thereof will not be repeated.

As shown in FIG. 8, the washing machine may comprise a cabinet 110, an outer tub 120 horizontally installed in the cabinet 110, an inner tub 190 rotatably installed in the outer tub 120, and an inner tub planarized unit 220 formed by planarizing an outer surface of the inner tub 160 such that concave-convex portions in an axial direction can be reduced, so as to restrain air noise from being generated during the rotation of the inner tub 160.

As shown in FIG. 9, the inner tub 190 may include a cylindrical portion 192 having a certain diameter, and a rear end portion 202 perpendicularly disposed at the rear end of the cylindrical portion 192.

The rear end portion 202 of the inner tub 190 may include an end surface 203 perpendicularly disposed with respect to the cylindrical portion 192, an insertion portion 204 recessed into the end surface 203 such that a frame 211 can be inserted therein from the outside, and a plurality of protrusions 205 backwardly protruding from the end surface 203. A plurality of through holes 206 are formed through each protrusion 205 such that inside and outside thereof can be connected.

The frame 211, as shown in FIGS. 9 to 11, may be configured such that both ends of its sectional surface are bent to be in contact with side surfaces of the insertion portion 204 and a central portion thereof protrudes to the outside.

The inner tub planarized unit 220 may include a plurality of guides 221 arranged outside the protrusions 205. The guides 221 are configured to block the other area of the rear end portion 202 of the inner tub 190 except for the insertion portion 204, namely, to block the protrusions 205 and the end surface 203.

Each guide 221 may include a plane portion 223, and a side wall portion 226 aligned with a side wall of the insertion portion 204 of the plane portion 223. A plurality of screw bosses 227 are formed at the side wall portion 226 such that the corresponding guide 221 can be coupled to the inner tub 190 by screws 228. Here, the insertion portion 204 may be configured such that another frame 181 having the shape as shown in FIG. 6 can be inserted therein. Here, the frame 181 may be implemented such that an outer surface thereof can be substantially coplanar with the outer surface of the guide 221.

In accordance with the configuration, when the frame 211 is coupled to the insertion portion 204, each guide 221 is attached to cover the corresponding protrusion 205 formed at the outer surface of the rear end portion 202 of the inner tub 190 to be coupled together by using the screws 228. Each of the guides 221 can reduce the noise due to air flow during the rotation of the inner tub 190.

Hereinafter, a washing machine in accordance with a third embodiment of the present invention will be described with reference to FIGS. 12 and 13. As shown in FIGS. 12 and 13, the washing machine may comprise a cabinet 110, an outer tub 120 horizontally installed in the cabinet 110, an inner tub 230 rotatably installed in the outer tub 120, and an inner tub planarized unit 250 formed by planarizing an outer surface of the inner tub 230 such that concave-convex portions in an axial direction can be reduced, to restrain air noise generated during the rotation of the inner tub 230.

The inner tub 230 may include a cylindrical portion 233, and the rear end portion 235 perpendicularly disposed at the rear end of the cylindrical portion 233. A frame 241 having a rotation shaft 243 is coupled to a rear end portion 235 of the inner tub 230. The rear end portion 235 of the inner tub 230 may include an end surface 236 perpendicularly disposed with respect to the cylindrical portion 233, an insertion portion 237 recessed into the end surface 236 such that the frame 241 can be inserted therein from the outside, and a plurality of protrusions 238 backwardly protruding with respect to the end surface 236.

The inner tub planarized unit 250, as shown in FIG. 12, may include a frame cover 255 coupled to spaces among the protrusions 238 such that an outer surface thereof can be substantially coplanar with the surface where the protrusions 238 are formed. A shaft opening 258 is formed through the center of the frame cover 255 such that the rotation shaft 243 can be inserted therein.

The frame cover 255 may include a plate portion 256 having an outer shape in correspondence with the spaces among the protrusions 238, and side wall portions 257 bent from the plate portion 256 to be in contact with the side surfaces of the protrusions 238.

In accordance with such configuration, when the frame 241 is inserted into the insertion portion 237, the frame cover 255 is inserted such that the rotation shaft 243 can be received in the shaft opening 258 in the center of the frame cover 255. After the complete insertion, the side wall portions 257 of the frame cover 255 are closely coupled to the side surfaces of the respective protrusions 238. The outer surface of the frame cover 257 is substantially coplanar with the surface where the protrusions 238 are formed. Accordingly, the frame cover 255 can reduce the generation of air flow during the rotation of the inner tub 230 and also prevent or reduce noise due to air flow by decreasing the air flow resistance.

Hereinafter, a washing machine in accordance with a fourth embodiment of the present invention will be described with reference to FIGS. 14 to 16. As shown in FIG. 14, the washing machine may comprise a cabinet 110, an outer tub 320 horizontally installed in the cabinet 110, an inner tub 160 rotatably installed in the outer tub 320, a planarized unit 330 formed by planarizing either an inner surface of the outer tub 320 or an outer surface of the inner tub 160, which face each other, such that concave-convex portions in an axial direction can be reduced, so as to prevent or reduce noise due to air flow during the rotation of the inner tub 160.

The outer tub 320 is installed in the cabinet 110, and the inner tub 160 is rotatably installed in the outer tub 320. A driving motor 128 for rotating the inner tub 160 is coupled to a rear end portion of the outer tub 320.

The planarized unit 330 may include an outer tub planarized unit 331 formed at an inner surface of the rear end portion of the outer tub 320, and an inner tub planarized unit 170 formed at an outer surface of the rear end portion of the inner tub 160.

The inner tub planarized unit 170 may be implemented, as shown in the description related to FIGS. 5 to 7, that the rear end portion 172 of the inner tub 160 is formed by being perpendicularly planarized at the rear side of the cylindrical portion 233 of the inner tub 160, and the insertion portion 177 is formed by recessing the rear end portion 172 of the inner tub 160 such that the frame 181 can be inserted therein, wherein the frame 181 has the rotation shaft 185 at the center of its outer surface, and the outer surface of the frame 181 is substantially coplanar with the outer surface of the rear end portion 172 of the inner tub 160. Here, as shown in the description related to FIGS. 8 to 11, the inner tub planarized unit 170 may be implemented as the inner tub planarized unit 220 configured by coupling the plurality of guides 221 to the outer side of the rear end portion 202 of the inner tub 190.

Also, as shown in the description related to FIGS. 12 and 13, the inner tub planarized unit 170 may be implemented as the inner tub planarized unit 250 configured by coupling the frame cover 255 to the insertion portion 237 of the inner tub 230.

In the meantime, the outer tub 320 may include a cylindrical portion 322, and the rear end portion 326 formed to block the rear side of the cylindrical portion 322.

As shown in FIG. 15, the outer tub planarized unit 331 may be configured by planarizing the inner surface of the rear end portion 325 of the outer tub 320, namely, by not forming a recess portion as shown in FIG. 2. A shaft opening 326 is formed at the center of the rear end portion 325 of the outer tub 320 such that the rotation shaft 185 of the frame 181 can be inserted therethrough.

A plurality of ribs 332 as shown in FIG. 16 may be formed at the outer surface of the rear end portion 325 of the outer tub 320 in order to prevent a decrease in a strength of the outer tub 320 which is caused by planarizing the inner surface of the outer tub 320 in order to form the outer tub planarized unit 331. The ribs 332 may include a plurality of first ribs 333 radially arranged in a radial direction of the outer tub 320, and a plurality of second ribs 334 formed in a circumferential direction of the outer tub 320 to cross the first ribs 333.

In accordance with such configuration, the outer tub planarized unit 331 and the inner tub planarized unit 170 may prevent or reduce air flow generation during the rotation of the inner tub 160 and also prevent or reduce noise due to air flow by reducing the air flow resistance.

Hereinafter, a washing machine in accordance with a fifth embodiment of the present invention will be described with reference to FIGS. 17 to 19. As shown in FIG. 17, the washing machine may comprise a cabinet 110, an outer tub 350 horizontally installed in the cabinet 110, an inner tub 160 rotatably installed in the outer tub 350, an outer tub planarized unit 390 formed at an inner surface of a rear end portion 365 of the outer tub 350, and an inner tub planarized unit 170 formed at an outer surface of a rear end portion of the inner tub 160.

The outer tub 350 is installed in the cabinet 110, and the inner tub 160 is rotatably installed in the outer tub 350. The outer tub 350 may include a cylindrical portion 362, and the rear end portion 365 configured to block the rear side of the cylindrical portion 362. A driving motor 128 for rotating the inner tub 160 is coupled to the rear end portion 365 of the outer tub 350.

As shown in the description related to FIGS. 5 to 7, the inner tub planarized unit 170 may be implemented such that the rear end portion 172 of the inner tub 160 is perpendicularly formed to block the rear side of the inner tub 160, and the insertion portion 177 recessed into the rear end portion 172 of the inner tub 160 is formed such that the frame 181 can be inserted therein, wherein the frame 181 has the rotation shaft 185 at the center of its outer surface, and the outer surface of the frame 181 is substantially coplanar with the outer surface of the rear end portion 172 of the inner tub 160.

Here, as shown in the description related to FIGS. 8 to 11, the inner tub planarized unit 170 may be implemented as the inner tub planarized unit 220 configured by coupling the plurality of guides 221 to the outer side of the rear end portion 202 of the inner tub 190. Also, as shown in the description related to FIGS. 12 and 13, the inner tub planarized unit 170 may be implemented as the inner tub planarized unit 250 configured by coupling the frame cover 255 to the insertion portion 237 of the inner tub 230.

Meanwhile, plane portions 371 and recess portions 372 recessed below the plane portions 371 may be formed at the inner surface of the outer tub 350. Each of the recess portions 372 may include linear ribs 374 protruding from a lower surface of the recess portion 372 to linearly extend in a radial direction of the outer tub 350, and a plurality of arcuate ribs 376 protruding from a lower surface of the recess portion 374 to extend by a certain length in a circumferential direction.

The outer tub planarized unit 390, as shown in FIG. 18, may be configured by coupling a plurality of covers 391 to cover the recess portions 372 such that the outer surface of the outer tub planarized unit 390 can be substantially coplanar with the surface where the plane portions 371 are formed.

As shown in FIG. 19, each of the covers 391 may include a body 393 having a fan shape in correspondence with the shape of the recess portion 372, and a plurality of screw coupling portions 394 configured such that the body 393 can be coupled to the recess portion 372 by screws 395.

In accordance with such configuration, the outer tub planarized unit 390 and the inner tub planarized unit 170 may prevent or reduce air flow generation during the rotation of the inner tub 160 and also prevent or reduce noise due to air flow by reducing the air flow resistance.

Hereinafter, a washing machine in accordance with a fifth embodiment of the present invention will be described with reference to FIGS. 20 to 22. As shown in FIG. 20, the washing machine may comprise a cabinet 110, an outer tub 350 horizontally installed in the cabinet 110, an inner tub 230 rotatably installed in the outer tub 350, an outer tub planarized unit 410 formed by planarizing an inner surface of a rear end portion 365 of the outer tub 350, and an inner tub planarized unit 430 formed by planarizing an outer surface of a rear end portion 235 of the inner tub 230.

The outer tub 350 is installed in the cabinet 110, and the inner tub 230 is rotatably installed in the outer tub 350. The outer tub 350 may include a cylindrical portion 362, and the rear end portion 365 configured to block the rear side of the cylindrical portion 362. A driving motor 128 for rotating the inner tub 230 is coupled to the rear end portion 365 of the outer tub 350.

Plane portions 371 forming plane surfaces and recess portions 372 recessed below the plane portions 371 may be formed at the inner surface of the rear end portion 365 of the outer tub 350, as shown in FIG. 21. Each recess portion 372 may include linear ribs 374 protruding from a lower surface of the recess portion 372 to linearly extend in a radial direction of the outer tub 350, and arcuate ribs 376 protruding from a lower surface of the recess portion 372 to extend by a certain length in a circumferential direction of the outer tub 350.

The outer tub planarized unit 410 may be configured by coupling an outer tub disc 411 to the inner surface of the rear end portion 365 of the outer tub 350 so as to block the recess portions 372. The outer tub disc 411 has a decreased diameter so as to be accommodated in the outer tub 350, and has a shaft receiving portion 413 formed through its center to receive the rotation shaft 243 of the inner tub 230. Screw bosses 415 are formed at the outer tub disc 411 to correspond to screw coupling portions 367 formed at the recess portions 372 of the outer tub 350. Screw openings 417 are formed through the respective screw bosses 415 such that screws 368 coupled to the respective screw coupling portions 367 can be inserted therein. Here, the outer tub planarized unit 410 may be implemented as one of the outer tub planarized units 331 and 390 as shown in the description related to FIGS. 14 to 19.

In the meantime, the inner tub 230 may include a cylindrical portion 231 and a rear end portion 235 configured to block the rear end of the cylindrical portion 231. The cylindrical portion 231 has a plurality of through holes 232 such that inside and outside of the cylindrical portion 231 can communicate with each other. A plurality of lifts 233 are disposed in the cylindrical portion 231. A frame 241 having the rotation shaft 243 is coupled to the rear end portion 235 of the inner tub 230.

As shown in FIG. 22, the rear end portion 235 of the inner tub 230 may include an end surface 236 perpendicularly disposed with respect to the cylindrical portion 231, an insertion portion 237 recessed into the end surface 236 such that the frame 241 can be inserted therein from the outside, and a plurality of protrusions 238 protruding in a rear direction with respect to the end surface 236. Each protrusion 238 has a plurality of through holes 239 such that inside and outside thereof can be connected.

The inner tub planarized unit 430 may be configured by coupling an inner tub disc 431 to an outer surface of the rear end portion 235 of the inner tub 230. The inner tub disc 431 may include a body 432 having a disc shape to block the rear end portion 235 of the inner tub 230, and a cylindrical portion 442 protruding in a thickness direction from an outer circumference of the body 432 to extend in a circumferential direction. A shaft receiving portion 433 is formed in the center of the body 432 such that the rotation shaft 243 can be received therein. A plurality of through holes 437 in correspondence with the through holes 239 of the protrusions 238 are formed through the body 432. Screw openings 435 are formed through the body 432 such that screws 247 coupled to screw coupling portions 245 formed at the frame 241 can be inserted therein. Here, the inner tub planarized unit 430 may be implemented as one of the inner tub planarized unit 170, 220 and 250 as shown in the description related to FIGS. 5 to 13.

In accordance with such configuration, the outer tub planarized unit 410 and the inner tub planarized unit 430 may prevent or reduce air flow generation during the rotation of the inner tub 230 and also prevent or reduce noise due to air flow by reducing the air flow resistance.

As described above, the illustrated embodiments of the present invention can provide the washing machine in which noise generation due to air during the rotation of the inner tub can be prevented or reduced either by generating air flow between the outer tub and the inner tub which make a relative motion with each other or by reducing air resistance.

Also, the illustrated embodiments of the present invention can decrease a load of a driving motor which rotates the inner tub by reducing air resistance which acts as a load during the rotation of the inner tub.

In addition, the illustrated embodiments of the present invention can prevent or reduce air-bone noise during the rotation of the inner tub without increasing fabricating cost by adapting a simple configuration instead of a significant change in the existent configuration.

It should be noted that although the illustrated embodiments only show a front-loaded washing machine, the present invention can also applies to a top-loaded washing machine where the inner tub and outer tub are vertically installed in the cabinet.

The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims. 

1. A washing machine comprising: a cabinet; an outer tub installed in the cabinet; an inner tub rotatably installed in the outer tub; and a planarized unit configured to planarize at least one of an inner surface of the outer tub and an outer surface of the inner tub, the inner surface of the outer tub and the outer surface of the inner tub facing with each other.
 2. The washing machine of claim 1, wherein the planarized unit comprises an outer tub planarized unit formed at a rear end portion of the outer tub.
 3. The washing machine of claim 2, wherein the outer tub planarized unit is configured to planarize an inner surface of the rear end portion of the outer tub, and a plurality of ribs are formed at an outer surface of the rear end portion of the outer tub.
 4. The washing machine of claim 2, wherein the outer tub planarized unit is configured to couple covers to a plurality of recess portions recessed into the inner surface of the rear end portion of the outer tub.
 5. The washing machine of claim 2, wherein the outer tub planarized unit is configured to couple an outer tub disc to the inner surface of the rear end portion of the outer tub.
 6. The washing machine of claim 1, wherein the planarized unit comprises an inner tub planarized unit formed at an outer surface of a rear end portion of the inner tub.
 7. The washing machine of claim 6, wherein the inner tub planarized unit is configured to planarize the outer surface of the rear end portion of the inner tub, and the inner tub planarized unit has an insertion portion recessed into the outer surface of the rear end portion of the inner tub such that a frame with a rotation shaft can be inserted therein.
 8. The washing machine of claim 7, wherein the outer surface of the frame is substantially coplanar with the outer surface of the rear end portion of the inner tub.
 9. The washing machine of claim 7, wherein the frame has a plurality of ribs protruding toward the insertion portion.
 10. The washing machine of claim 6, wherein a plurality of protrusions protrude at the outer surface of the rear end portion of the inner tub, and the inner tub planarized unit is configure to couple a plurality of guides to block the protrusions.
 11. The washing machine of claim 10, wherein an insertion portion in which the frame with the rotation shaft is coupled is formed between the protrusions, and wherein the inner tub planarized unit further comprises a frame cover coupled to insertion portion to block the frame.
 12. The washing machine of claim 6, wherein the inner tub planarized unit is configure to couple an inner tub disc to the outer surface of the rear end portion of the inner tub.
 13. The washing machine of claim 6, wherein the outer tub is horizontally installed in the cabinet.
 14. A washing machine comprising: a cabinet; an outer tub installed in the cabinet; an inner tub rotatably installed in the outer tub; an outer tub planarized unit configured to planarize an inner surface of a rear end portion of the outer tub; and an inner tub planarized unit configured to planarize an outer surface of a rear end portion of the inner tub.
 15. The washing machine of claim 14, wherein the outer tub planarized unit is configured to planarize the inner surface of the rear end portion of the outer tub when configuring the outer tub, and a plurality of ribs are disposed at the outer surface of the rear end portion of the outer tub.
 16. The washing machine of claim 15, wherein the outer tub planarized unit is configured to couple covers to a plurality of recess portions recessed into the inner surface of the rear end portion of the outer tub.
 17. The washing machine of claim 14, wherein the outer tub planarized unit is configured to couple an outer tub disc to the inner surface of the rear end portion of the outer tub.
 18. The washing machine of claim 14, wherein the inner tub planarized unit is configured to planarize the outer surface of the rear end portion of the inner tub, and the inner tub planarized unit has an insertion portion recessed into the outer surface of the rear end portion of the inner tub such that a frame with a rotation shaft can be inserted therein.
 19. The washing machine of claim 18, wherein the outer surface of the frame is substantially coplanar with the outer surface of the rear end portion of the inner tub.
 20. The washing machine of claim 18, wherein the frame has a plurality of ribs protruding toward the insertion portion.
 21. The washing machine of claim 14, wherein a plurality of protrusions protrude at the outer surface of the rear end portion of the inner tub, and the inner tub planarized unit is configure to couple a plurality of guides to block the protrusions.
 22. The washing machine of claim 21, wherein an insertion portion in which the frame with the rotation shaft is coupled is formed between the protrusions, and wherein the inner tub planarized unit further comprises a frame cover coupled to insertion portion to block the frame.
 23. The washing machine of claim 14, wherein the inner tub planarized unit is configured to couple an inner tub disc to the outer surface of the rear end portion of the inner tub.
 24. The washing machine of claim 14, wherein the outer tub is horizontally installed in the cabinet. 